Phosphatidylinositol 4-kinase: gene structure and requirement for yeast cell viability.

Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Science (Impact Factor: 31.48). 12/1993; 262(5138):1444-8. DOI: 10.1126/science.8248783
Source: PubMed

ABSTRACT Phosphatidylinositol (PtdIns) 4-kinase catalyzes the first step in the biosynthesis of PtdIns-4,5-bisphosphate (PtdIns[4,5]P2). Hydrolysis of PtdIns[4,5]P2 in response to extracellular stimuli is thought to initiate intracellular signaling cascades that modulate cell proliferation and differentiation. The PIK1 gene encoding a PtdIns 4-kinase from the yeast Saccharomyces cerevisiae was isolated by polymerase chain reaction (PCR) with oligonucleotides based on the sequence of peptides derived from the purified enzyme. The sequence of the PIK1 gene product bears similarities to that of PtdIns 3-kinases from mammals (p110) and yeast (Vps34p). Expression of PIK1 from a multicopy plasmid elevated PtdIns 4-kinase activity and enhanced the response to mating pheromone. A pik1 null mutant was inviable, indicating that PtdIns4P and presumably PtdIns[4,5]P2 are indispensable phospholipids.

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    ABSTRACT: Abstract Phosphatidylinositol lipids are signaling molecules involved in nearly all aspects of cellular regulation. Production of phosphatidylinositol 4-phosphate (PI4P) has long been recognized as one of the first steps in generating poly-phosphatidylinositol phosphates involved in actin organization, cell migration, and signal transduction. In addition, progress over the last decade has brought to light independent roles for PI4P in membrane trafficking and lipid homeostasis. Here, we describe recent advances that reveal the breadth of processes regulated by PI4P, the spectrum of PI4P effectors, and the mechanisms of spatiotemporal control that coordinate crosstalk between PI4P and cellular signaling pathways.
    Critical Reviews in Biochemistry and Molecular Biology 11/2013; 49(1). DOI:10.3109/10409238.2013.853024 · 5.81 Impact Factor
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    ABSTRACT: Phosphatidylinositol 4-OH kinase III (PI-4K) is involved in the regulated local synthesis of phospholipids that are crucial for trans-Golgi network (TGN)-to-plasma membrane trafficking. In this study, we show that the calcium sensor proteins calneuron-1 and calneuron-2 physically associate with PI-4K, inhibit the enzyme profoundly at resting and low calcium levels, and negatively interfere with Golgi-to-plasma membrane trafficking. At high cal-cium levels this inhibition is released and PI-4K is activated via a preferential association with neuronal calcium sensor-1 (NCS-1). In accord to its supposed function as a filter for subthreshold Golgi calcium transients, neuronal overexpression of calneuron-1 en-larges the size of the TGN caused by a build-up of vesicle proteins and reduces the number of axonal Piccolo-Bassoon transport ves-icles, large dense core vesicles that carry a set of essential proteins for the formation of the presynaptic active zone during develop-ment. A corresponding protein knockdown has the opposite effect. The opposing roles of calneurons and NCS-1 provide a molecular switch to decode local calcium transients at the Golgi and impose a calcium threshold for PI-4K activity and vesicle trafficking. calcium binding protein 7 caldendrin neuronal calcium sensor-1 phosphatidylinositol 4-OH kinase III calcium binding protein 8 P hosphoinositides are low-abundant, negatively-charged phos-pholipids that are crucially implicated in the regulation of intracellular vesicle trafficking and exocytosis (1, 2). The levels of individual phosphoinositides are controlled by specific lipid kinases, whose activities and localization are in turn regulated by a variety of effectors (1). Phosphatidylinositol 4-OH kinase III (PI-4K) is an enzyme that acts on phosphatidylinositol (PI) in the generation of phosphatidylinositol 4-phosphate (PIP), which is not only thought to be the rate-limiting step in the production of phospha-tidylinositol 4,5-bisphosphate (PIP2), but seems to be a second messenger in its own right (3). A number of PIP and PIP2 binding proteins have been identified that are crucially involved in Golgi-to-membrane trafficking and in endo-and exocytosis (1–4). Ac-cordingly, PI-4K was shown to be essential for Golgi-to-plasma membrane transport (1–4). The passage of proteins along the secretory pathway is also regulated by intracellular calcium (Ca 2) gradients (5–7), and the Golgi apparatus is an established Ca 2 microdomain containing Ca 2 release and sequestration apparatuses. Ca 2 signals within the Golgi microdomain are transduced into regulatory events via Ca 2 -binding proteins that are either directly or indirectly attached to the Golgi membrane. Surprisingly little is known, however, about the underlying molecular mechanisms of Golgi Ca 2 signal trans-duction. It is therefore unclear why elevated Ca 2 levels are needed for the exit of vesicles from Golgi. Studies so far have showed that the neuronal calcium sensor-1 (NCS-1) via its N-terminal myris-toylation associates in a Ca 2 -independent manner with Golgi membranes (8, 9) where it interacts with PI-4K (10, 11). This interaction appears to be an evolutionary highly-conserved mech-anism that has evolved already in yeast (10, 12). Yeast null mutant strains of Frequenin, the Drosophila (13)/yeast orthologue (10) of NCS-1, and those of the yeast PI-4K orthologue Pik1 are not viable, pointing to the essential role of both proteins in Golgi-to-plasma membrane trafficking (10, 14–16). This finding is, however, at variance with the situation in mammalia where NCS-1 seems to be more diffusely distributed in neurons with considerable amounts of the protein localized outside of the Golgi (17, 18). Moreover, its binding to PI-4K seems to be of lower affinity as compared with the yeast proteins (11). It is therefore likely that the regulation of Pik1 and PI-4K differs substantially with the latter being more susceptible to modulation via Ca 2 transients at the Golgi (19). To date, NCS-1 is the only NCS protein known to interact with PI-4K, whereas other members of this family, like Recoverin (10) or KChIP (16), apparently do not modulate PI-4K activity. Based on their similarity to the synaptic Ca 2 sensor caldendrin (20) we have identified a subfamily of NCS proteins termed calneuron-1 and calneuron-2 (Fig. S1 A and ref. 21). In contrast to classical NCS proteins, calneurons do not contain a N-terminal myristoylation site and their EF-hand organization differs substantially from that of other family members (Fig. S1 A and refs. 21 and 22). In the present report we show that both calneurons are regulators of PI-4K and trans-Golgi network (TGN)-to-plasma membrane trafficking in neurons.
    Proceedings of the National Academy of Sciences 04/2009; · 9.81 Impact Factor
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